There is a growing trend in the aerospace industry to expand the use of composite materials for a diverse array of structural and dynamic applications. One particular application for the use of composite materials lies in the fabrication of main rotor blades for helicopters.
With increased usage of composite materials to fabricate main rotor blades, the helicopter industry is continually seeking to improve the tooling and/or methods used to fabricate main rotor blades so as to reduce the per unit fabrication costs associated with the main rotor blades or to improve the tolerances of the fabricated main rotor blades. Per unit fabrication costs may be higher than need be where a particular fabrication protocol involves the use of multiple tools and/or extensive set up times. Or, perhaps even more importantly, per unit fabrication costs, repeatability, and/or blade tolerances may be adversely impacted to greater or lesser degrees to the extent that the fabrication protocol involves manual labor.
Sikorsky Aircraft has developed a parallel manufacturing protocol for fabricating helicopter main rotor blades wherein a blade subassembly and a leading-edge sheath are concurrently fabricated as individual components, and then the prefabricated blade subassembly and the prefabricated leading-edge sheath are integrated in combination to form an assembled main rotor blade. The assembled main rotor blade is subsequently cured to form a finished main rotor blade. This protocol was adopted in large measure because experience has shown that the leading edges of main rotor blades are subjected to varying degrees of abrasion during helicopter operations. As a consequence of such abrasion effects, the leading edge of a helicopter main rotor blade at stone point becomes aerodynamically unsuitable for further use. Rather than replacing the entire main rotor blade, it was determined that a replaceable leading-edge sheath would allow abrasion-degraded main rotor blades to be efficaciously and economically repaired.
The manufacturing protocol for fabricating the prefabricated leading-edge sheath involves a fabrication procedure wherein a cured leading-edge sheath having an oversized configuration is formed in a conventional composite molding process, i.e., assemblage of the components of the leading-edge sheath on a sheath mold assembly and subsequent curing to form the cured leading-edge sheath. By forming the cured leading-edge sheath in an oversized configuration, the assemblage process is greatly simplified since the lay-up tolerances of the composite material incorporated in the leading-edge sheath need not be layed-up to precise tolerances. In addition, the finished edges of the prefabricated leading-edge sheath have a relatively complex span wise profile to accommodate the asymmetric spanwise twisting and chordwise displacements of the main rotor blade. The tolerances of the finished edges must be closely maintained to ensure that the prefabricated leading-edge sheath may be properly integrated in combination with the blade subassembly to form the main rotor blade. Forming the finished edges in the composite plies that are part of the leading-edge sheath prior to the assemblage procedure increases the risk that the precise tolerance of the finished edges will not be maintained during subsequent curing and/or handling of the leading-edge sheath.
The oversized configuration of the cured leading-edge sheath requires that the cured leading-edge sheath be further worked to form the finished edges thereof. The prior art procedure for forming the finished edges in the cured leading-edge sheath involves the scribing or marking of trim lines in the cured leading-edge sheath, the scribed trim lines defining the profiles of the finished edges of the prefabricated leading-edge sheath. To scribe the trim lines, the oversized, cured leading-edge sheath is removed from the sheath mold assembly and a trim bonnet having a V-shaped, latticed configuration corresponding to the cured leading-edge sheath is overlayed in aligned combination with and secured to the oversized, cured leading-edge sheath. The opposed edges of the trim bonnet define the profiles of the finished edges of the prefabricated leading-edge sheath. An operator moves a scriber against each opposed edge to scribe the trim lines in the oversized, cured leading-edge sheath. Once the trim lines are scribed, the trim bonnet is disengaged from the oversized, cured leading-edge sheath and removed therefrom, and the oversized, cured leading-edge sheath is cut along the scribed trim lines to form the prefabricated leading-edge sheath.
The prior art procedure for scribing the trim lines in the oversized, cured leading-edge sheath is disadvantageous in being heavily labor intensive. This increases the probability that the trim lines may be improperly scribed, for example due to a misalignment in securing the trim bonnet to the oversized, cured leading-edge sheath, or due to human error during physical scribing of the sheath. Further, the scribing procedure is time consuming inasmuch as the oversized, cured leading-edge sheath must be removed from the sheath mold assembly, the trim bonnet must be manually overlayed and secured in combination with the oversized, cured leading-edge sheath, the scribing procedure is effectuated manually, and the trim bonnet must be manually disengaged and removed from the oversized, cured leading-edge sheath. Moreover, continued handling of the trim bonnet increases the risk that the profiled edges thereof will be inadvertently damaged or the tolerances thereof lost, leading to improperly scribed trim lines.
A need exists to provide an apparatus and procedure that minimizes the human involvement in scribing trim lines in an oversized, cured leading-edge sheath. The apparatus should simplify the set up procedures for use of the apparatus. The apparatus should provide increased accuracy and repeatability in scribing trim lines in cured leading-edge sheaths. The apparatus should be configured to simultaneously scribe trim lines on both sides of the cured leading-edge sheath.